5 replies to this topic

[enricosavazzi]

The Osram Ultra Vitalux 300W is a relatively cheap (as UV sources go) lamp that can be operated in a normal ceramic E27 socket, directly fed with 230 V AC mains power. I have not found a precise description of this type of lamp, other than the large glass bulb contains a much smaller high-pressure arc bulb (halogen? mercury? mercury-halogen? other?) and a couple of electronic components visible from the rear of the bulb. The emitted light is visually quite yellowish.

The specifications say that this lamp emits 13.6 W of UVA and 3W of UVB. The remaining 284 W of VIS, NIR and IR of course generate a lot of heat. Nonetheless, the amount of UVA and UVB is far more than what we get from normal UV LED torches and UV CFLs. This is both good (for UV imaging) and bad (for our protection), and filtering out all that VIS is of course a main concern.


The spectrum of this lamp (blue line) shows several tall spikes (probably from Hg emission, although I did not check all of them) superposed on a roughly gaussian distribution centered around 630 nm. Therefore, the UVA emission is continuous (in the sense that there are no emission gaps) but uneven across the range. This means, in practice, that it is possible to use this source for spectroscopic measurements of transmission and reflection across all, or almost all, the UVA range, as long as you compensate in post-processing for the uneven emission (and this happens to be the purpose I had in mind). Reducing the heat and VIS to acceptable levels still remains a challenge, but it is feasible if one does not need high amounts of UV and/or large irradiated surfaces.

I threw in also a spectrum from a quartz xenon tube (red line), to show how different the two sources are. The xenon tube is of course a better UV source if your spectroscope can record a flash source, but the Osram Ultra Vitalux is so far the potentially most usable continuous source for UV and VIS I tested so far, without going for deuterium lamps.

PS - This lamp is not approved for suntanning in humans (it is mainly marketed for horse solariums and reptile enclosures). However, googling shows that some people use it for suntanning, as a cheaper alternative to solariums.

[Vagabond]

Thank you very much for this detailed review and for the spectrum of the lamp Enrico!!

Cheers,

Nicola

[Andrea B.]

I have added a link to <> Sticky :: UV Photography Intro, Cams, Mods, Lights, Links <>.

[DonPilou]

Hi,
After having read this topic, I ordered 2 bulbs 2 weeks ago to compare them to the Omnilux 105W. I was really disappointed by the UV emission: the bulb offers really strong visible light but few UV light, like 5-6 times less than the Omnilux bulb.

[Cadmium]

Enrico, How do these compare with the typical spiral 'black light', and even the UVB reptile lights?
I seem to get a fairly wide range UV-A from my spiral black light.

[enricosavazzi]

I have not compared side-by-side, but I checked the emission spectrum of a typical small (9 W or 11 W) "black light" spiral bulb time ago. I cannot find the graph right now, but I do remember that emission was concentrated on the strongest Hg lines, with just a hint of an underlying continuous emission (probably by a phosphor coating inside the tube). The Ultra Vitalux clearly has a continuous emission spectrum superposed to a few strong lines.

Then the other big difference is VIS intensity. The Ultra Vitalux is blindingly bright in the VIS, while "black-light" tubes have a built-in VIS-cut coating.

If I had to choose a source with a continuous UV spectrum (for example to measure transmission spectra of filters and lenses), I would choose the Ultra Vitalux. "Black light" tubes (or at least the one I tested) have large emission gaps in the UV spectrum, which make them unsuitable as a UV source for spectroscopy. Emission gaps make it impossible to produce a reliable absorption graph - essentially, in the lack of a real signal, the graph displays only amplified noise in correspondence of the emission gaps. This is false data and easily leads to erroneous interpretations.

Deuterium lamps are often used in transmission UV spectrometers because they have a very continuous spectrum, in spite of the fact that they emit only minuscule amounts of UV. This makes it easier to filter away noise, since knowing in advance that the spectrum is homogeneous makes it possible to predictably interpolate intensity at a given point even in the presence of noise.

If discontinuous Hg emission lines with large gaps are acceptable, on the other hand, it is entirely possible for a "black light" tube to emit more UV than a halogen arc, since emission is concentrated at those lines. It is also much easier to get rid of the VIS and NIR emission of these tubes, e.g. for UV-stimulated fluorescence.

I Googled the Omnilux 105 W tubes, but they are discontinued at local sellers. I don't know whether they are still produced.